double-whammy waste heat (charger heats motor and inverter)

[jray3]

I don't like the idea of battery charger waste heat being used to 'preheat' the inverter and drive motor, especially during summer. Stock flow paths run the coolant from pump to charger, inverter, motor, radiator, tank, then back to the pump.
Anybody thought about re-plumbing that circuit so that coolant hits the radiator before the motor?
Simply reversing the flow would put motor heat into the more-fragile inverter, so not a good thing.
Options I've thought of thus far would be

A: a bypass valve to shunt coolant around the inverter and motor during charging. It would need to have a failsafe such that coolant follows the original path in the event of a valve problem, and continues cooling a hot motor and inverter during charging.

B: a second coolant pump for the bypass so that the battery charger thermostat activates pump #2, while the original pump runs according to the motor and inverter signals. This could be done without any electronics hacking by teeing into the coolant lines and running pump #2 with a standalone thermoswitch that comes on at a lower temperature than the OEM controls. (or runs continuously off 120 VAC during charging, tapped from the J1772 cabling). Experimental observation or the addition of backflow preventers would be required to ensure that no unintended short-circuited coolant flows occur. (such as a loop back thru the motor and inverter, with no flow in the charger and radiator during charging!)

Next to put some numbers to the driving efficiency losses from charging waste heat and determine if this would be at all worthwhile....

 

[PV1]

I've noticed this, but never really thought about changing it. Maybe a bi-directional pump? When the car runs the pump, it runs like normal, but when plugged in, a reversing relay (probably solid-state) engages to either run a separate or a bi-directional pump so that the coolant runs in reverse after 30 minutes of charging, for example. This way, the pumps runs normal during charging for 30 minutes so that the motor can cool without cooking the inverter, then the coolant switches direction so that the motor and inverter cool nearly completely with cool coolant from the radiator. The heat generated by the charger goes directly to the radiator.

https://www.dropbox.com/s/q5ondpbo2lfqb7a/i-MiEV%20coolant%20loop.png

 

[Don]

This isn't something I would want to mess with, unless I understood a lot more about what the Mitsu engineers were trying to accomplish with the way they designed things. I have a very high regard for 99% of the way they designed this car and my feeling is that an amateur engineer changing anything might be a step in the wrong direction

JMO of course - Let me know how it works out! Great discoveries are made every day by those willing to risk life and limb . . . . or in this case, the warranty on their car :lol:

Don

 

[siai47]

You need to look at what is being done with the cooling system. Remember, the charger is part of the heat into the coolant loop but along with it, the DC-DC convertor is also in operation powering the DC systems in the car. So, the waste heat has to go somewhere. To cool those two components, the heat must be radiated somewhere. In the I-MiEV, that happens by dissipating the heat through other components in the loop including the inverter and the drive motor and radiator. The radiator fan doesn't need to operate during normal charging which might not be the case if the coolant loop didn't include other components as "radiators". Operating the fan would increase the DC load on the system during charging which would reduce charging efficiency. I think that's what is really going on here. I have used a small fan to direct air through the front radiator during charging and it is surprising how cool all of the system components actually stay. BTW--in some other EV charging systems (old AC propulsion systems and others) the motor windings are actually used as part of a bi-directional inverter/charger system and therefore need to be in the cooling loop.